Question: Compute $1011_2 + 101_2 - 1100_2 + 1101_2$.  Express your answer in base 2.
Explanation: $1011_2 + 101_2 - 1100_2 + 1101_2 = (1011_2 + 101_2) + (-1100_2 + 1101_2) = 10000_2 + 1_2 = \boxed{10001_2}$.